This invention relates to polyvinyl chloride series resin compositions which permit small amounts of additives, particularly plasticizers, to be dissolved out and exert harmful effect on the blood.
Hitherto, a large variety of additives have been used with polyvinyl chloride series resin compositions. Particularly, a plasticizer has been added in large quantities to soften the polyvinyl chloride resin. Where such type of polyvinyl chloride resin is applied, for example, to food containers and medical products in particular, those additives have been selected which are as harmless as possible to the human body. However, some of said additives may be proved to exert a harmful effect on the human body by subsequent studies and experiments. Therefore, the additives contained in polyvinyl chloride resin compositions should preferably be prevented from leaching under any condition in which said resin are applied.
A plasticizer, for example, generally consists mainly of phthalic acid ester. Where articles made of polyvinyl chloride series resin compositions containing said phthalic acid ester as a plasticizer are brought into contact with water, said plasticizer is known to be gradually leached out into the water. Though phthalic acid ester leached out into the living body has not been definitely ascertained to have a harmful effect on the health of said living body, yet prevention of the leaching of said plasticizer assumes great importance from the medical point of view.
On the other hand, the nonmigratory plasticizer which has been produced in the past has the drawbacks that it renders polyvinyl chloride series resin compositions less workable due to its high viscosity, has a large molecular weight, is easily saponified because it generally belongs to the polyester series, and is difficult to soften. Therefore, the nonmigratory type of plasticizer is not adapted for use with polyvinyl chloride series resin compositions applied as medical products and food containers.
It is accordingly the object of this invention to provide polyvinyl chloride series resin compositions which prevent additives, particularly, a plasticizer contained therein from being dissolved out, exert little harmful effect on the blood and can be safely applied as food containers, beverage vessels and medical products, and also to provide medical products formed of said polyvinyl chloride series resin compositions and a method of manufacturing said resin compositions.
The present inventors have discovered that incorporation of silicone oil together with the conventional additives in polyvinyl chloride series resin compositions prominently prevents said additives from being dissolved out.
The invention is characterized by impregnating polyvinyl chloride series resin compositions with 0.2 to 7 parts by weight, based on the polyvinyl chloride series resin composition, of at least one kind of silicone oil selected from the group consisting of polymethyl phenyl siloxane, polydimethyl siloxane, polydiphenyl siloxane, polydimethyl methylphenyl siloxane, polydimethyl diphenyl siloxane and polymethyl hydrogen siloxane.
The method of manufacturing polyvinyl chloride series resin compositions according to this invention consists in previously emulsifying silicone oil with part of a plasticizer, adding the remainder of the plasticizer to the resin compositions and thereafter thermally blending both masses. The term polyvinyl chloride series resin, as used herein, means polyvinyl chloride, polyvinylidene chloride, copolymers (including terpolymers) formed mainly of vinyl chloride with a minor amount of other commoner and polymer blends containing polyvinyl chloride as a main component. Comonomers capable of forming copolymers of polyvinyl chloride include vinylidene compounds such as vinyl ester, vinyl ether and vinylidene chloride, lower olefins, vinyl acetate, vinyl bromide, vinyl fluoride, aromatic compounds (for example, styrene), cyclic unsaturated compounds (for example, vinyl pyridine), acrylic acid and derivatives thereof, and conjugate unsaturated compounds such as butadiene.
Other polymers being blended with polyvinyl chloride include styrene-acrylonitrile copolymer and styrene-methylmethacrylate copolymer.
Silicone oil being added to polyvinyl chloride series resin compositions is at least one compound selected from the group consisting of polydimethyl siloxane, polymethyl hydrogen siloxane, polydiphenyl siloxane and polymethyl phenyl siloxane. When directly mixed with polyvinyl chloride series resin compositions, silicone oil having low affinity therefor can not be fully dispersed in said resin compositions. Therefore, it is advised first to emulsify silicone oil with a plasticizer having good affinity therefor and add said emulsion to the polyvinyl chloride series resin compositions. This process enables silicone oil to be fully dispersed in said resin compositions and be coated on the surface thereof.
The proportion of silicone oil is chosen to be 0.2 to 7 parts or preferably 1 to 4 parts by weight based on the added amount of a polyvinyl chloride series resin. Smaller addition of silicone oil than 0.2% by weight fails fully to prevent additives including a plasticizer from being dissolved out. Conversely, larger addition of silicone oil than 7% by weight presents difficulties in molding and processing polyvinyl chloride series resin compositions and fails to provide a homogeneous product of said resin compositions due to the low miscibility of silicone oil therewith.
The proportion of a plasticizer is chosen to be 20 to 80 parts by weight based on 100 parts by weight of polyvinyl chloride series compositions. It is generally preferred to add a larger amount of silicone oil with increase in the proportion of the plasticizer.
For the object of this invention, it is possible to select the kind and proportion of additives including a plasticizer in the same manner as in the past. Silicone oil which itself concurrently acts as a lubricant eliminates the necessity of adding any particular lubricant to polyvinyl chloride series resin compositions.